Electronic trigger



May l, 1951 A. H. DlcKlNsoN l2,551,103

- ELECTRONIC TRIGGER Original Filed May 23, 1941 ATTORNEY Patented May l, 1951` ELECTRONIC TRIGGER Arthur EDickinson, Greenwich, Conn., assignor to International Business Machines lllorpora` 'trionk New York, N. Y., a corporation o! New Application June 28, 1947, Serial No. 757,766, which is a division of application, Serial No. 394,881, May 23, 1941. Divided and this application August 24, 1948, Serial No. 45,924

2 claims. (ci. 25o-27) One of the objects of the present invention is to provide a trigger circuit operable to one con-4 dition and back to an initial condition and timing means determining the time duration of one of said conditions.

Another object is to provide a. novel trigger circuit of two inherent stable conditions comprising a triodeand a multi-grid electronic de "vice for establishing one `of said stable conditions and a triode andra multi-grid electronic device for establishing the other of said stable conditions.

Still another object is to provide a novel trigger circuit comprising a pair of cross-coupled triodes and a multi-grid electronic device for each of said triodes for selectively rendering its triode effective.

Still a further object is to provide a novel trigrvger circuit operative 'to either of two conditions vprovided with selection .means to determine which condition will be assumed by said trigger.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of examples, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. 1 is a basic wiring diagram of the novel trigger circuit employed inthe invention.

Fig. 2 is a wiring diagramof a modication of the trigger circuit of Fig. l.

Referring to the drawings and more particularly to Fig.. 1, this discloses a basic circuit comprislng vacuum tubes interconnected by resistances and condensers, as shown. Two triodes of the four vacuum tubes shown are so interconnected in a trigger unitand operate in such a manner that the trigger assumes two conditions of stability. When one of the triodes is conducting, .a large amount of current ows through it and the other triode is at shut-off. In

other words, in one condition of stability, one of the triodes has a relatively low impedance and the other has a relatively high impedance. In the other condition o'i stability, the respective conditions of the two triodes is reversed. Controlling impulses are applied to the other two vacuum tubes, which are pentodes, comprising the trigger unit to cause the shift from one condi- Y tion of stability to the other. Every second impulse brings the trigger to the original condition of stability. I

Referring to Fig. 1, voltage of the polarity indicated is supplied to lines 50 and 5| and to a voltage divider consisting of resistances 56 and 51. Voltage is also supplied by means of the divider to line 6l, its potential being positive with respect to line 5I.

The trigger circuit comprises two impedance networks. One network includes-resistances 62a, 63a and 64a, resistance 63a being shunted by coupling condenser 65a. Vacuum tubes 68h and 69h shown in one envelope, in Fig. 1, are connected in parallel between point 66a, located between resistances 62a and 63a, and line 6I. The second impedance network consists of resistances 62h, 63h, and 64b, resistance 63h being shunted by coupling condenser 6511./ Vacuum tubes 68a and 69a, also shown in one envelope in Fig. 1 are connected in parallel between point 66h, located between resistances B2b and 63h, andy line 6l. Resistances .62a and 62h are equal in value as are resistances 63a and 63h, and resistances 64a and 64b. The capacities of condensers 65a and 65h are also equal. In actual practice an eicient combination was found when the values of resistances 62a and 64a were each approximately one-third the value of resistance 63a. A suitable value for the capacity of the condenser 65a is of the order of a few hundred micromicrofarads.

Assuming that the grid of triode 68a is substantially at the same potential as line 6l, its grid bias will be substantially zero. With resistance B2b properly chosen, triode 68a has an impedance relatively low as compared to that of resistance B2b and its anode and point 66h to which the anode is connected will have a voltage which is not much greater than that of line 6I with large current flow through triode 68a. With` resistances 63h and 64b properly chosen,

the potential drop across 63h is great enough to maintain pointtlb and hence the grid of triode 68h, negative with respectto line 6|. With triode 68h negatively biased, it has an impedance greater than that of resistance 62a. Hence the anode of triodetab and point 66a to which the anode is connected are at a high enough potential so that the voltage drop across resistance 63a will not force the potential of point 61a below that of line 6 I.

The foregoing describes one conditiorrgof stability in which triode 68a has a large current now therethrough and triode 68h is at shut-ofi, hence with no current now therethrough, and point 66a is at a higher potential with respect to lines 6I and 5I, than is point 66h. The manner of switching the trigger circuit to the other condition of stability, is as follows.

In order to shift the trigger from one stable condition to the other, pentodes 69a and 69h may be employed. The screen grid (hereinafter designated as a screen) of pentode 69a is connected to a point on a voltage divider consisting of resistors 10a and lla. The potential of this point being positive with respect to line 6I,

the screen voltage of pentode 69a is positive with respect to its cathode.'v The screen of pentode 69h is connected to a point on a, voltage divider consisting'of resistors 10b and 1lb. The voltage of this point is likewise positive with respect to -llne 6I, so that the screen potential of pentode 69h is positive with respict to its cathode. The

'control grid (hereinafter designated as the grid) of pentode 69a is connected to the control grid of 69h and both are connected to a resistance 12, to which positive pulses are applied in a manner described, for example, in application Serial No. '757,766 led June 28, 1948.

In the absence of any pulse on resistor 12, the negative grid bias of pentodes 69a and 69h is-the potential difference betweenlines 6| and 5| and is sufficiently great to maintain pentodes 69a and 69h at shut-oil.

When, however, a positive pulse is applied to resistance 12, there is a simultaneous negative bias reduction of the grids of both pentodes 69a and 69h, but since the anode of pentode 69a is directly connected to that of triode 68a and since the plate voltage of triode 68a and point 66h is very low, this particular bias reduction is ineective to increase current ilow through pentode 69a and thus has no eiect on the trigger circuit. The anode of pentode 69h, however, is directly connected to that of triode 68h and to point 66a, and since the potential of this point, with respect to line 6l, is relatively high, the simultaneous Abias reduction of pentode 69h causes a current flow as follows: From line 50, resistor 62a, pentode 69h, line 6I, resistance 51 to line 5I, thus causing point 66a to suddenly drop in potential, producing a negative pulse. This negative pulse is fed through condenser 65a to the grid of triode 68a, eiectlng a sudden increase in the negative grid bias thereof, and reducing current flow through triode 68a and resistance 62h. Point 66h, accordingly, rises in potential, with respect to line 6I, to produce a positive pulsewhich is fed through condenser 65h to the grid of triode 68h, changing its grid bias to substantially zero. Since now the potential of point 66D has risen and that of point 66a has dropped, triodes 65a and 68h assume another condition of stability-which is the reverse of that originally described, namely, triode 68a is now shut-oil while triode 68h passes a large amount of current. the trigger circuit will be maintained until another positive pulse is applied to resistance 12. When this occurs, the resulting negative grid bias reduction of pentode 69h is ineffective while that of pentode '69a is `effective to increase cur- This new status of rent flow therethrough, and the trigger is returned to the condition of stability originally described.

It may be noted that to best achieve the operations as described above, theVy pulses applied to the grids of pentodes 69a and 69h should be of steep wave form. Preferably the R. C. product of the value of resistance 12 and the value of the capacity of any associated condenser should not exceed one-fifth the R. C. product of resistance 63a and condenser 65a. It should also be noted, that negative pulses, applied to the grids of pentodes 69a and 69h, are ineffective, to cause the shifting action explained above, in the particular vtrigger just described.

Novel means are now provided for rendering the trigger action selective. In the foregoing description, it is assumed that switches 13a and 13b are in open position, as shown. The closure of switch 13a. shunts out a portion of resistance 1 la, thus reducing the screen potential of pentode 69a to substantially thatof line 6I. Assuming that the trigger condition of stability is such that point 66h is at a high potential, this screen potential reduction prevents any negative grid bias reduction of pentode 69a from being effective in bringing about increased current flow therethrough. Therefore, until switch 13a is opened, successive applications of positive pulses to resistance 12 are ineffective to change the status of the trigger from that condition in which points 66h and 66a are at high and low potentials, respectively.

Similarly, the closure of switch 13b shunts out a portion of resistance 1lb, thus reducing the screen voltage of 'pentode 891i to substantially` that of line 6|. Such screen voltage reduction, when point Elia is at high potential, prevents any negative grid bias reduction of pentode 69h from being effective in bringing about increased current flow therethrough. Therefore, under these conditions, until switch 13b is opened, successive applications of positive pulses to resistance 12 are ineffective to change the status of the trigger from that condition in which points 66a and 66h are at high and low potentials, respectively. Switches 13a and 13b, therefore, comprise parts of selection means whereby selectivity in operation is obtained.

The condition ofthe trigger maybe determined by observation of a glow discharge (neon) tube 18, which is connected in series with a current limiting resistor, between line and point 66a. When point 56a is at a high potential with respect to line 6|, the diierence in voltage between it and line lis insuflicient to ignite tube 18. When point 66a, however, is at a low potential (point 66h at high potential), the difference in voltage is great enough to cause neon'tube 18 to fire. This indicates that the trigger, as a whole, is on.

That portion of the circuit of Fig. l within the broken line enclosure nds extensive use in various portions of the electronic pulse producer of application Serial No. 757,766 led- June 28, 1948.

For purposes of simplicity, this enclosed portion will be hereinafter termed a trigger element and it will also be understood as described in connection with the ignition of neon tube 18 that when points Sib and 66a are respectively at high and low potentials, with respect to lines 6l and 5I, the trigger element is on an on status and that when the potentials 0f points 66h and 66a are respectively low and high, with respect to lines 6l and 5l, the trigger element is in an off status. The voltages which exist at'poirlts The circuit of Fig. 2 also relates to a trigger- I ing circuit, which is substantially similar to that just described in connection with Fig. 1. Portions of this circuit, which correspond in character and function to portions of the circuit of Fig. l, are given the same reference characters. With regard to the arrangement of Fig. 2, it also may have two conditions of stability, but in lieu of deriving pulses from a common source and applying them to two circuit points to shift the condition of stability, two sources of pulses, such as resistances 12a and 12b are employed. It is assumed that such pulses do not occur simultaneously. The grid of pentode 69a is connected to resistance 12a and whenever a positive pulse,

occurring at one time, on 12a is applied to the` grid of 69a, there is an increased current flow through 69a, assuming that triodes 68a and 68h have high and low impedances, respectively, and the circuit shifts to a. stable condition in which points 66h and 66a are at low and high potentials, respectively. With the circuit in this last status, a positive pulse occurring, at another time, on resistor 12b reduces the negative grid bias of pentode 69h causing increased current ilow therethrough and the trigger is shifted to the opposite condition of stability, wherein points 66h and 66a are at high and low potentials, respectively, or in other words the trigger, as a whole, is on. TheV manner in which the circuit shifts from one condition of stability to the other is similar to that described in connection with the circuit in Fig. 1. Selection means, as in the circuit of Fig. 1, are provided, since it is obvious that closure of switch 13a (Fig. 2) prevents pulses applied to resistor 12a from being effective while the closure of switch 13b prevents pulses applied to resistor 'I2-b from being effective. Manipulation of switches 13a and 13b, therefore, permits selective operation of the circuit. This modification of the triggering circuit, which includes the two sources of pulses, is employed extensively in the circuits of the electronic pulse producer of said application Serial No. 757,766. That portion of ,the Fig. 2 circuit within the broken line enclosure, is identical in structure to that portion in Fig. 1 within the `broken line, except that the control grids of pentodes 69a and 69h are not interconnected. This portion, therefore, is called a trigger element, and it, along with its two sources of pulses forms the basis of the electronic commutatgr described in said application Serial No. 757,76

While tubes v69a and 69h have been shown as pentodes in the circuits of Figs. 1 and 2, it will be understood that one or both of these vacuum tubes may be triodes, like tubes 68a and 68h. When' tubes 69u and 69h are triodes, however, no screen grids are available to afford the trigger circuit the novel feature of selectivity provided by the selection means as set forth above.

Novel electronic trigger means having two conditions of equilibrium are therefore provided and novel means are also provided in combination' therewith for producing selective controlof a selectedone of said conditions.

' While there have been shown and described and pointed out the fundamental novel features of the invention as applied to preferred embodimentspit will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated and in their operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.v Y

What is claimed is:

1. An electronic trigger comprising a pair of tubes cross-coupled to form a. trigger having two conditions of equilibrium, a multi-grid tube in parallel with one of said pair of tubes and switching means connected to a grid of said multigrid tube for altering the bias thereon for selectively determining which of said conditions of equilibrium will be assumed.

2. An electronic trigger comprising a pair of triodes, means electrically cross coupling the input of each of said triodes and the output of the other of said triodes, a pentode connected in shunt with each of said triodes and switching means connected to a grid of each of said pentodes for selectively determining which sustained condition of said trigger will be assumed when pulses are applied to said trigger.

ARTHUR H. DICKINSON.

" REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Name Date Mathes Nov. 6, 1934 Kahn Mar. 19, 1935 Koch Aug. 4, 1936 Koch er May 16, 1939 Reeves Feb. 3. 1942 OTHER REFERENCES Review of Scientic Instruments, vol. 8, November 1937, A Vacuum Tube Circuit for Scaling Counting Rates by Stevenson et al., pases 414-416.

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